Let's assume that Nazi Germany would have had the crazy idea to offer the United States the possibility of exchanging population, in the way that the US would receive the Jews, Roma, Slavs etc. etc. the Nazis did not want in their own and conquered territories like if they were new immigrants to be resettled in America, while the US in its side would strip the citizenship of lots of German/Austrian immigrants or other citizens of German origin using the excuse of a potential 'treason' to America, forcing them to 'return' to Germany (thus the loss of population in the Nazi German territories would be more or less compensated).
Of course the idea might be unacceptable at first for the US government, but the pressure of leaving those millions of people in Europe under the high risk of becoming victims of a potential genocide or other atrocities when they could have the chance of saving all of them without having to send American soldiers to die there...would not be that easy to reject at the end. Of course the Nazis would guarantee the Americans that all the German-American people returned to Europe would be well treated (as they were interested in keeping them as a productive workforce and provide them jobs, farms etc.).
Of course the idea might be unacceptable at first for the US government, but the pressure of leaving those millions of people in Europe under the high risk of becoming victims of a potential genocide or other atrocities when they could have the chance of saving all of them without having to send American soldiers to die there...would not be that easy to reject at the end. Of course the Nazis would guarantee the Americans that all the German-American people returned to Europe would be well treated (as they were interested in keeping them as a productive workforce and provide them jobs, farms etc.).